Soldato
I will see if I can find some engine usage stats, but I wouldn't be surprised to find that most cars will have used 2 engines within the first 4 flyaway races, where the cars don't return to base.
I don't doubt that - in the past they have generally try to use a new engine at Monza and Spa too (though its highly unlikely they can with only 4 to start with).
But if this loophole has existed since the rules were introduced, they've had more than a year to plan the updates for this season and how and when to introduce them, so there's nothing to say they won't just try to use 1 engine for the first quarter of the season if the upgrade to the 2nd engine will bring in sufficient performance improvements, and so on for the rest of the season.
If the FIA are going to allow this but exclude Honda why not give Honda the opportunity to use 5 engines this season, as the others were last, and then allow Honda the entire 2016 season to do in-season upgrades? You know it's not going to happen though.